Pope Honorius III in the context of "Duchy of Estonia (1219–1346)"

The Order of Preachers (Latin: Ordo Prædicatorum, abbreviated OP), commonly known as the Dominican Order, is a Catholic mendicant order of pontifical right that was founded in France by the Castilian priest Dominic de Guzmán. It was approved by Pope Honorius III via the papal bull Religiosam vitam on 22 December 1216. Members of the order, who are referred to as Dominicans, generally display the letters OP after their names, standing for Ordinis Praedicatorum, meaning 'of the Order of Preachers'. Membership in the order includes friars, nuns, active sisters, and lay or secular Dominicans (formerly known as tertiaries). More recently, there have been a growing number of associates of the religious sisters who are unrelated to the tertiaries.

Founded to preach the gospel and to oppose heresy, the teaching activity of the order and its scholastic organisation placed it at the forefront of the intellectual life of the Middle Ages. The order is famed for its intellectual tradition and for having produced many leading theologians and philosophers. In 2018, there were 5,747 Dominican friars, including 4,299 priests. The order is headed by the master of the order who, as of 2022, is Gerard Timoner III. The Blessed Virgin Mary, Mary Magdalene, Augustine of Hippo and Francis of Assisi are the Principal Patrons of the order.

Pope Innocent IV (Latin: Innocentius IV; c. 1195 – 7 December 1254), born Sinibaldo Fieschi, was head of the Catholic Church and ruler of the Papal States from 25 June 1243 to his death in 1254.

Fieschi was born in Genoa and studied at the universities of Parma and Bologna. He was considered in his own day and by posterity as a fine canonist. On the strength of this reputation, he was called to the Roman Curia by Pope Honorius III. Pope Gregory IX made him a cardinal and appointed him governor of the Ancona in 1235. Fieschi was elected pope in 1243 and took the name Innocent IV. He inherited an ongoing dispute over lands seized by the Holy Roman Emperor, and the following year he traveled to France to escape imperial plots against him in Rome. He returned to Rome in 1250 after the death of the Emperor Frederick II.

Oliver of Paderborn, also known as Oliver Scholasticus or Oliver of Cologne (c. 1170 – 11 September 1227), was a German cleric, crusader and chronicler. He was the bishop of Paderborn from 1223 until 1225, when Pope Honorius III made him cardinal-bishop of Sabina. He was the first Paderborn bishop to become a cardinal. Oliver played a significant role in the Crusades as a preacher, participant and chronicler.

Pelagio Galvani (c. 1165 – 30 January 1230, Portuguese: Paio Galvão Latin: Pelagius) was a Leonese cardinal, and canon lawyer. He became a papal legate and leader of the Fifth Crusade.

Born at Guimarães, his early life is little known. It is repeatedly claimed that he entered the Order of Saint Benedict but this is not proven. Pope Innocent III created him cardinal-deacon of Santa Lucia in Septisolio around 1206. Later, he was promoted to the rank of cardinal-priest of S. Cecilia (probably on 2 April 1211), and finally opted for the suburbicarian see of Albano in the spring of 1213. He subscribed the papal bulls between 4 May 1207 and 26 January 1230. He was sent on a diplomatic mission to Constantinople in 1213. During this two-year mission he attempted to close Orthodox churches and imprison the clergy, but this caused such domestic upset that Henry of Flanders, the Latin Emperor of Constantinople, reversed his actions which had caused the "tempest which held the city of Constantine in its grip", as noted a contemporary historian. Three years later he was elected Latin Patriarch of Antioch but his election was not ratified by the Holy See. He was dispatched in 1218 by Pope Honorius III to lead the Fifth Crusade at Damietta in Egypt, and made a poor strategic decision in turning down favourable peace offers made by the sultan al-Kamil. During his absence, the see of Albano was administer by Thomas of Capua.

Religiosam vitam is the incipit designating a papal bull issued on 22 December 1216 by Pope Honorius III. It gave universal recognition to the Dominican Order. The order already had monasteries in Rome, Paris and Boulogne and had already been locally recognized by the bishop of Toulouse the year before – its creation had coincided with the Albigensian Crusade in southern France, in whose support the Dominicans had been very active. It adopted the Rule of St Augustine, but was also regulated by rulings and decisions taken by its own regular general chapters.

The Duchy of Estonia (Estonian: Eestimaa hertsogkond, Danish: Hertugdømmet Estland, Latin: Ducatus Estoniae), also known as Danish Estonia, was a direct dominion (Latin: dominium directum) of the King of Denmark from 1219 until 1346 when it was sold to the Teutonic Order and became part of the Ordensstaat.

Denmark rose as a great military and mercantile power in the 12th century. It had an interest in ending the frequent Estonian attacks that threatened its Baltic trade. Danish fleets attacked Estonia in 1170, 1194, and 1197. In 1206, King Valdemar II and archbishop Andreas Sunonis led a raid on Ösel island (Saaremaa). The Kings of Denmark claimed Estonia, and this was recognised by Pope Honorius III. In 1219, the fleet of Valdemar II landed in the harbor of Lindanise (Tallinn) and defeated the local Estonians in the Battle of Lindanise. This brought northern Estonia under Danish rule until the Estonian uprising in 1343, after which the territories were taken over by the Teutonic Order. They were sold by Denmark in 1346.